Study on photocatalytic activity of ZnO nanoneedles, nanorods, pyramids and hierarchical structures obtained by spray pyrolysis method Deniss Klauson a,n , Inga Gromyko b , Tatjana Dedova b , Natalja Pronina a , Marina Krichevskaya a , Olga Budarnaja a , Ilona Oja Acik b , Olga Volobujeva b , Ilmo Sildos c , Kathriin Utt c a Department of Chemical Engineering, Tallinn University of Technology, Ehitajate tee 5,19086 Tallinn, Estonia b Department of Materials Science, Tallinn University of Technology, Ehitajate tee 5,19086 Tallinn, Estonia c University of Tartu, Institute of Physics, Riia 142, 51014 Tartu, Estonia article info Keywords: Zinc oxide Hierarchical Spray pyrolysis Photocatalytic activity abstract In this research, ZnO nanostructured layers with various morphology, i.e. nanoneedles, nanorods, pyramid shaped ZnO crystals, and hierarchical structures of ZnO deposited on nanorods and pyramid shaped crystals, were synthesised by pneumatic spray pyrolysis method. Hierarchical structures, a dense network of well-ordered platelets covering the side facets of the rod-like and pyramid shaped ZnO crystals, were obtained by spraying Zn (Ac) 2 solution over the surface of pre-grown ZnO crystals at deposition temperature of 330 1C within 5 min. All ZnO layers have been characterised by scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), absorbance of ultraviolet and visible light (UV–vis), surface wettability measurements and photoluminescence (PL). Photocatalytic activity of the layers was evaluated by means of photocatalytic oxidation activity (PCO) of several organic pollutants, namely, methyl-tert-butyl ether (MTBE), humic acid (HA), N,N-dimethyl p-nitrosoaniline (RNO), and prednisolone (PNL); the results were compared to the performance of well-established commercial photocatalyst, P25 titanium dioxide (Evonik). MTBE was the most efficiently degradable compound by all objects, while RNO was effectively degraded by plain structures only. In HA photocatalysis, needle-like ZnO as the most efficient material; PNL was the least degradable by ZnO layers. In the degradation of MTBE, RNO and HA, ZnO objects have shown activity comparable to or highly exceeding that of P25 TiO 2 . The explanation of the differences in ZnO objects' photoactivity is proposed to be the different character of oxidising species produced by the ZnO objects, and different interactions of these with the degradation substrates, based on the relative amount of surface defects, surface morphology and hydroxylation of the ZnO structures' surface. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction The interest in the preparation of ZnO nanostructures such as nanowires, nanorods, hierarchical structures of ZnO is continuously growing due to the wide potential of their applications in optoelectronic devices, gas sensors, or Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/mssp Materials Science in Semiconductor Processing http://dx.doi.org/10.1016/j.mssp.2014.12.012 1369-8001/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ372 620 2851; fax: þ372 620 2856. E-mail address: deniss.klauson@ttu.ee (D. Klauson). Materials Science in Semiconductor Processing 31 (2015) 315–324